This invention relates generally to motor-containing devices such as pumps, power tools and the like, and more particularly, to means for improving the dissipation of motor-generated heat in such devices.
Numerous devices are known that utilize electric motors to produce useful mechanical motion. For example, many liquid pumps are powered by electric motors. Power tools typically employ electric motors to rotate, reciprocate, or vibrate a tool member that operates on a work piece. In devices of this type, it is common to mount the motor within a protective housing. Operation of the motor results in the generation of heat within the housing. The amount of heat generated depends upon such factors as the motor efficiency, the time periods of continuous motor operation and the mechanical load on the motor. Under various conditions, the rate at which heat is generated by the motor can exceed the rate at which the heat is dissipated through the walls of the housing. As the heat accumulates within the housing, the temperature of the motor and of components adjacent thereto increases. Continued operation of the device under such conditions can, and frequently does, result in serious damage to the motor and other components of the device.
Internal heating problems of the above type are particularly troublesome in devices, such as submersible pumps, in which the motor is enclosed within a sealed or liquid-tight housing. Ideally, in such devices, the motor should be mounted so that the motor casing is in direct contact with the internal surface of the housing walls to facilitate direct heat conduction to the housing walls whence it is dissipated in the liquid surrounding the housing. In practice, however, because of manfacturing tolerances and other considerations such as ease and economy of assembly, a gap inevitably remains between the motor casing and the internal housing surface. This gap, even if relatively small, typically contains stagnant air which insulates the motor and resists the transfer of heat to the housing walls. Such stagnant air gaps make sealed devices quite susceptible to overheating and has accounted for many premature device failures.